Northern Rivers residents have been warned there may be a scorcher of a Sunday on the way.

A severe heatwave will hit many parts of inland Australia for the rest of the week, with temperatures in the high 30s predicted for Friday and Saturday on the NSW north coast.

ABC North Coast weather expert and former Bureau of Meteorology forecaster Steve Symonds says temperatures could hit 40 on the Northern Rivers on Sunday.

"There is a big high pressure system out in the Tasman Sea and that's going to hang around for a while," he said.

"Then it's going to move west and join up with another trough that's going to move through on about Sunday.

"Between today and Sunday we're going to have north-north westerly winds coming straight down off the hot interior of Australia and that's going to bring temperatures in the high 30s and it's going to get hotter on Friday, Saturday and into Sunday.

"Sunday could be an absolute scorcher depending on when that trough moves through... Sunday is going to be a nasty one."